This invention relates to the support trunnions of rotary dryers and drum mixers. More specifically, this invention relates to self-aligning trunnions to provide full contact between trunnion support rollers and the trunnion rings encircling a rotatable cylindrical dryer or drum mixer such as used in soil reclamation, quarry and asphalt plant operations.
Drying and mixing equipment for these types of plant operations generally comprises a large diameter steel cylinder drum circumscribed by two steel tires, known as trunnion rings, with one being mounted toward each end of the cylinder. The cylinder is supported in a substantially horizontal position by four steel carrying rollers or trunnions. Power to rotate the cylinder upon the trunnions is provided either by motors driving the trunnion rollers or by a separate system which drives the cylinder directly through a ring and pinion gear or a sprocket and chain.
Alignment of the trunnions is critical. Ideally the axis of rotation of each trunnion roller should be parallel to the axis of rotation of the rotary drum and its associated trunnion rings. When parallel, the mating surfaces of the trunnion rollers and rings are in full contact promoting uniform wear and maximizing power transmission. However, since most rotary drums and dryers are slightly inclined (typically 3 to 6 degrees from horizontal) to facilitate transporting the process material within the drum from one end to the other, there is a need to control the resulting horizontal downhill thrust load on the equipment. The industry has, heretofore, accomplished this by slightly skewing the trunnion rollers, relative to the trunnion rings, to create a compensating uphill thrust. Barrier or thrust rollers are commonly added in close proximity to the uphill and downhill side of one or more of the trunnion rings as a fail-safe to keep the dryer from walking longitudinally off the trunnion rollers in either the uphill or downhill direction. Alternatively, flanges may be incorporated at each end of the trunnion rollers to capture the trunnion ring therebetween and to prevent the drum from walking off the trunnion rollers when there is horizontal movement.
The industry is plagued with problems associated with the practice of skewing the trunnions. Accurate alignment is extremely difficult for several reasons. First, precise measurements of a few thousandths of an inch on a drum or dryer that may be from 6 to 12 feet in diameter and from 30 to 60 feet in length, and even larger in the case of cement kilns, is difficult in itself even under the best of circumstances given the manufacturing tolerances to which such large scale equipment can be built. Second, the degree to which the trunnions must be skewed actually changes depending on whether the drum is loaded or unloaded, and even on the amount of load. Generally, the greater the load the greater the response to any skewing of the trunnions. With too much skew the drum will ride hard uphill. With insufficient skew the drum will ride hard downhill. Third, the actual shape of the drum and trunnion rings can change with thermal expansion at different temperatures causing variation in the response to skewing of the trunnions. Alignment, and more specifically correct alignment, is a constant operational problem because it is ever changing.
Another problem associated with the practice of skewing the trunnions is that the power requirement to rotate the drum increases as the trunnions are skewed from a parallel alignment with the drum. When the trunnions are skewed, full bearing with the trunnion ring is reduced with a resulting loss in power transmission when the drum is trunnion driven. Additionally, trunnions are often individually skewed in ways that work in opposition to each other. That is, one trunnion may be forcing the drum uphill while another is influencing it downhill. This condition is common because quick adjustments to resolve a problem of the drum walking too hard, either uphill or downhill, often involves adjusting just one trunnion. Theoretically, and for best operation, all four trunnions should remain parallel with one another and, therefore, each should be adjusted identically. In actual practice, however, it is much easier for the maintenance personnel to adjust just one trunnion enough to accomplish the desired result of stabilizing the longitudinal travel of the drum. As these adjustments occur periodically and on various maintenance shifts over time, it often develops that the trunnions may be working against each other, and thereby creating a load which must be overcome with additional horsepower.
An additional problem is the often-excessive wear on the trunnion rings and the trunnions themselves induced by the skewing of the trunnions. When the trunnions are at odds with one another, as described above, significant wear will occur. Generally, this results in skipping or slipping of one or more of the trunnions relative to the face of the trunnion rings. This, in turn, results in a washboard wear pattern on the face of the trunnion ring, which after a period of time, can make the drum inoperable because of wear induced vibration.
A need remains in the industry for an improved multi-point support system for rotating drums and dryers to address the problems and drawbacks heretofore experienced with skewed trunnion rollers. The primary objective of this invention is to meet this need.